An axial flow gas turbine engine, such as an aircraft “jet-engine”, generally comprises an air inlet, a compressor section, a fuel combustion chamber, a turbine section, one or several rotatable drive shafts connecting corresponding compressors and turbines, an exhaust outlet and structures for supporting the drive shafts and for mounting the engine to, e.g., an aircraft.
The supporting structures are static parts that typically include an inner shell or ring, for connection to bearings and a centrally located drive shaft, and an outer shell or ring, for connection to, e.g., an engine casing, and where circumferentially distributed, load carrying airfoil shaped radial elements extend between and connect the inner and outer shells/rings. A primary axial gas flow through the engine thus flows through the areas formed between the rings and the elements.
It is known to bleed air/gas from gas turbine engines for generating a flow of pressurized air/gas that, for instance, can be used for pressurizing the airplane cabin or for cooling or heating purposes. As described in e.g., U.S. Pat. No. 2,986,231 and W095/04225, a flow of bleeding air can be generated by arranging additional non-structural radial elements across the gas flow and provide these (airfoil shaped) elements with some form of internal channel that connects an inlet located at the leading edge of the radial element in the primary axial gas flow and an outlet located at an outer part of the element.
It is also known to make use of a load carrying radial element of a supporting structure for leading the flow of bleeding air. However, because the supporting structures need to be capable of transferring considerable radial loads between the drive shaft and the engine casing and therefore require radial elements that have a significant stiffness, and because channels and openings for leading bleed air generally have a negative effect on the stiffness and strength of the elements, it is more complicated to make use of structural elements than non-structural elements for generating the flow of bleeding air.
Traditionally, supporting structures of the type discussed here are produced by casting, and there are various known ways of designing casted structures where the radial elements are capable of leading a flow of bleed air while at the same time exhibiting a sufficient strength and stiffness.
The desire for low-weight products in air-craft applications has generated a need for supporting structures that are less heavy than the traditional casted structures but that still are capable of transferring radial loads, withstanding an internal pressure etc. Generally, such low-weight structures are manufactured by joining, typically by welding, a number of prefabricated parts together. The radial elements of such prefabricated structures usually consist of hollow airfoil shaped vanes. A particular problem with regard to air bleeding channels arises where the vanes are formed by welding a first part of the vane to a second part that forms an extension of the first part so that the welded cross-sectional connection becomes located somewhere along the length of the vane. A typical example is when the first vane part form part of a casted inner ring (hub) to which the remaining, outer part of the vane and the outer ring are joined. How to arrange air bleeding channels and openings in such vanes is not evident since the air bleeding system must not interfere with the welding interface or reduce the structural stiffness of the vane.
In order to increase the possibilities of making use of lighter, prefabricated supporting structures there is a desire for designs that allow air bleeding.